1. Field of the Invention
The invention concerns: a radiation source for a radiation-based image acquisition device, having an electron emitter to generate a focal spot for x-ray generation at a rotating anode, as well as a radiation-based image acquisition device with such a radiation source, and a method to determine an asymmetrical power input profile of a focal spot of a radiation source parallel to a movement direction of a rotating anode of the radiation source.
2. Description of the Prior Art
Powerful radiation sources are needed today in many fields in which x-ray radiation is required, such as for imaging, particularly medical imaging Rotating anode x-ray tubes in which an electron beam is generated by means of an electron emitter (cathode) are known as radiation sources. This electron beam is accelerated through a vacuum toward a rotating anode by electrical fields. The impact point of the electron beam on the rotating anode is generally designated as a focal spot. The electrons braking in the anode generate x-ray radiation (characteristic radiation, bremsstrahlung). However, the efficiency is approximately 1%, meaning that 99% of the electrical energy is transduced into heat. In order to prevent melting of the anode, a rotating anode is used so that the focal spot “wanders” along the movement direction of the rotating anode, which means that a point is ever exposed only for a short time.
In order to obtain an optimally sharp and clearly defined x-ray beam, in modern radiation sources the focal spot has an optimally small expansion. However, the smaller the focal spot, the less electrical power can be transduced into radiation energy. The reverse applies, namely that the more power input that occurs at a narrow space in the rotating anode, the shorter the service life of the rotating anode. It is thus typical to optimize the design of the focal spot so that it is fashioned to be homogeneous over optimally wide areas (apart from edges at the border) so that temperature gradients that are too high do not occur. Ultimately the same power input thus ensues at every exposed point.